Method of treating cellulosic fibers with a cationic protein dispersion



Jim 1964' J. D. ROBERTSON ETAL 3,119,732

METHOD OF TREATING CELLULOSIC FIBERS WITH A CATIONIC PROTEIN DISPERSIONFiled May 1, 1961 PULP SLUE RY (ANIONIC) PROTEIN AcIb 4 PROTEIN ACID(CATIoNIc) 4 ALLJM PuLD- PROTEIN MIXTURE pH 4.5To 5.5

PAPER MACHINE Juuus b. EoaEIzTsoN and CHARLES N. BETTIS INVENTORSZ ByiyiUnited States Patent Ofiiee 3,11%,732 Patented Jan. 28, 1954 3,119,732METHOD OF TREATKNG CELLULOSIC FIBERS WETH A CATKONHC PRSTEIN DEYERSEQNJulius D. Robertson and Cixaries N. lBetts, Hartsviiie, 3.6., assignorsto Sonoco Products Company, Hartsviile, S.C., a corporation of douthCarolina Filed May 1, 1961, Ser. No. 1%,499 7 Claims. (Cl. 162-174) Thisinvention relates to a method of making paper and more particularly to amethod of treating paper pulp which is to be subsequently formed into apaper web.

In the making of paper, it has been proposed to add various materials tothe paper pulp prior to its being formed into a paper web so as toimpart certain highly desirable improved properties to the paper such asincreased strength and the like. It is well known that proteins makegood bonding agents and various proteins have been added to paper pulpduring the paper making process in order to promote fiber bonding andthereby obtain an improved paper product.

It has been recognized that the maximum fiber bonding obtainable withthe use of a protein additive to the paper pulp has not beenaccomplished as various limitations have been present which make itdifiicult to utilize the full fiber bonding potential of the protein.For instance, use has been made of soluble proteins such as animal gluebut soluble proteins do not produce the substantial increase in fiberbonding which it is desired to obtain. Insoluble proteins such as caseinhave been used as alkaline dispersions for beater additives withsubsequent precipitation by an acidic agent such as aluminum sulfate buthere again fiber bonding to the desired degree has not been obtainedwith such a process and the resulting paper product was somewhatdeficient in strength.

Accordingly, a primary object of this invention is to provide a new andnovel method for treating cellulosic fibers utilized in a paper makingprocess which produces a bond between the cellulosic fibers ofconsiderably greater strength than has been possible heretofore.

Another object of this invention is to provide a new and novel method oftreating paper pulp utilized in a paper making process which permitsfull utilization of the fiber bonding potential of proteins added topaper pulp.

A further object of this invention is to provide a new and novel methodof treating cellulosic fibers utilized in a paper making process whichresults in a paper product of high strength and which at the same timematerial-1y reduces the pollution load of the paper making effiuent.

Other further objects of the invention hereof will be apparent from thefollowing description of the methods and procedures utilized in theproduction of the end prodnot.

The accompanying drawing illustrates the process of the presentinvention in flow diagram form.

In general, the novel method of the invention is directed to a papermaking process in which paper pulp is prepared in the conventionalmanner as a slurry or suspension of fibers in an anionic condition at apH within the range of 5.0 to 8.0. Preferably the pH of the pulp slurryis within the range of 6.5 to 7.5. The 6.5 to 7.5 pH range of the paperpulp or cellulosic material slurry is a pH range at which pulp isgenerally produced in conventional paper making processes and theanionic condition of the paper pulp provides a negative electricalpotential on the pulp particles or fibers. However, it should beunderstood that a pH above or below this 6.5 to 7.5 range iscontemplated within the scope of the invention provided that the fibersare in an anionic condition.

In the description of the processes of this invention, the termcellulosic fibers is to be construed as defining either purifiedcellulose or cellulose of various degrees of lignification, ranging fromground wood to highly delignified chemical pulps. It should beunderstood that the methods of the invention may be used withoutstanding results for the treatment of any cellulosic fibrous materialwithin thse broad categories.

The novel method of the invention has as one of its objects the additionof a protein to cellulosic fibers or paper-pulp to enhance thefiber-to-fiber bonding. To this end, a protein is colloidally dispersedin water having a suitable mineral or organic acid added thereto so thatthe pH of the acid-aqueous protein dispersion is adjusted to a valuebelow the iso-electric point of the protein. Preferably the pH of thecolloidal protein dispersion is within the range of 1.5 to 2.5. Sincethe pH of the acid colloidal protein dispersion is substantially belowthe isoelectric point of the protein, the protein particles in thedispersion are cationically or positively charged.

The protein used in the practice of the method of the invention can beidentified generally as being amphoteric which term, its well known,identifies proteins capable of forming a colloidal dispersion with anacid to give a positively charged or cationic protein dispersion. By wayof example, proteins such as casein, Delta protein (a purified soybeanprotein), cotton seed protein, soybean protein and the like give highlysatisfactory results when used as described in the practice of theinvention.

The acid employed in the preparation of the colloidal protein dispersionmay be any suitable mineral or organic acid such as hydrochloric acid,acetic acid or formic acid.

The desired amount of the cationic protein dispersion is then mixed withthe pulp slurry. Preferably, the protein, in cationic dispersion, isadded to the pulp slurry in 7 an amount substantially less in proportionto the pulp by weight. Generally, the protein will be !1 0% andpreferably within the range of 0.1% to 5% of the weight of bone drypulp. The positive charges on the protein particles of the cationicprotein dispersion and the negative charges on the cellulosic fibers orpulp particles bring about a mutual discharge or neutralization of theelectrical charges, incipient flocculation of the paper pulp slurry, andacceleration of the rate of drainage and dewatering. The proteinmaterial from the colloidal dispersion is deposited or precipitated onthe cellulosic fibers. The resulting deposit of protein on the surfaceof the fibers presents a good interface for subsequent fiber-to-fiberbondmg.

The precipitation of the protein is then completed by adjusting the pHof the protein-fibers mixture to substantially the iso-electric point ofthe protein. Generally speaking, this iso-electric point will occur at apH within the range of between 4.5 to 5.5 or more specifically 4.5 to5.0. This adjustment of the pH may be accomplished in the conventionalmanner by the use of an acid or papermakers alum (aluminum sulfate).

For a better understanding of the present invention, representativeexamples were carried out and control paper handsheets for use in theseexamples were prepared as outlined below. These handsheets were used forcomparison purposes in Examples I, II, III below. The examples givenbelow illustrate the wide range and scope of the novel method of thisinvention.

Laboratory control paper handsheets were prepared by beating repulpednewsprint to a Schopper Freeness of 359 cc. to provide a pulp slurry.Portions of the pulp slurry were separated and Weighed and used toproduce handsheets having a caliper of 0.03 inch.

EXAMPLE I Laboratory handsheets for this example were made by firstpreparing an acid colloidal protein dispersion utilizing casein as theprotein dispersed in a weak hydrochloric acid solution to bring the pHof the dispersion to a value of 2.0. This casein, in acid dispersion,was added to weighed portions of this pulp slurry in an amountequivalent to approximately 1% of the weight of the bone dry pulp. Tothe protein-pulp mixture was added 1.25% (bone dry pulp basis)papermakers alum to adjust the pH of the mixture to approximately 4.5.Handsheets made from this protein-treated pulp were compared with thecontrol handsheets described above and the results are shown in Table Ibelow. It will be noted in this example that substantial increases inSchopper Freeness and Ring Crush were obtained with the proteinadditive.

Table I Hanclshects Containing Protein Additive Control HandslicctsEXAMPLE II The protein additive employed in this example was a highviscosity soybean protein in a hydrochloric acid colloical dispersion ata pH of 2.0. This protein, in acid dispersion, was added in an amountequivalent to approximately 1% of the weight of the bone dry pulp.Papermakers alum in an amount of 1.25% (bone dry pulp basis) was thenadded to the pulp to complete the precipitation of the protein at a pHof 4.5. Handsheets were formed from this protein-pulp mixture and testsresults performed thereon were compared with the tests results of thecontrol handsheets as shown in Table II. It will be noted in thisexample that substantial increases in Schopper Freeness and Ring Crushwere obtained with the protein additive.

Table II Handshccts Containing Protein Additive Control Handshccts M owto lo EXAMPLE III The protein used in this example was Kasoy 200 D whichis a soybean meal containing approximately 50% protein and is acommercially available product. The

Kasoy meal was prepared as an acid colloidal dispersion in the manner ofthe previous examples and added to the pulp in an amount equivalent toapproximately 3% of the weight of the bone dry pulp. The precipitationof the protein was then complet d with papermalters alum added to theKasoy 2G0 D-pulp mixture in an amount of 2% (bone dry pulp basis). Testsresults on laboratory handsheets prepared from Kasoy 2G0 D-pulp mixturewere obtained and were compared with the control handshcets of ExamplesI and II as shown in Table III below. Here again, substantial increasesin Schopper Freeness and Ring Crush were obtained with the Kasey 200 Dadditive.

In the two following examples, actual commercial paper making productionconditions were employed. Accordingly, paper was prepared on a papermachine under production conditions to produce a conventional paperwhich was used as a basis for comparison with other runs of papertreated in accordance with the invention.

EXAMPLE IV In this example, the protein additive was casein in acolloidal aqueous dispersion with hydrochloric acid. This casein, inacid dispersion, was added to a newsprint pulp slurry in an amountequivalent to 1% of the weight of the bone dry pulp. Then, 2% (bone drypulp basis) by weight of papermalters alum was added to the pulpproteinmixture to adjust the pH to approximate 4.5 and complete theprecipitation of the protein. The tests results on machine made paperprepared from the pulp slurry having a protein additive are comparedwith the machine made control paper without the additive and thesecomparative results are shown in Table IV below. No ditierence was notedin the Schopper Freeness tests results comparison but the Ring Crushresults were improved by the addition of protein to the paper.

EXAMPLE V Example V was carried out in a manner similar to Example IVusing a paper machine under production conditions to produce controlpaper and paper having added thereto a colloidal acid dispersion ofKasey 200 D (soybean meal) in an amount equivalent to 3% of the weightof the bone dry pulp. Test results performed on the paper made from apulp slurry having the protein additive were compared with the machinemade control paper and comparative tests results are shown in Table Vbelow. It will be noted that paper with the protein additive showed asubstantial increase in Schopper Freeness and in the 6" Ring rush ascompared with the control paper without the protein additivedemonstrating clearly the advantages gained by the novel method of theinvention.

Table V Machine Machine Made Paper Made Paper Without With KasoyAdditive 200 D Additive Type of Machine Cylinder Cylinder Type of PulpNewsprint Newsprint Number of Plies 6 6 Caliper of Paper (in). .025 O25pH of pulp slurry 6. 5-7. 5 4. 5 Percent Kasoy 200 D added to pul 0 3. 0Percent Paperrnakers alum added to pulp-Kasoy mixture 0 2.0 SchopperFrceness (ca)... 400 450 6 Ring Crush (lbs) 169 200 Five day BiochemicalOxygen Demand of paper machine effluent (parts per million) 718 460 Asshown in Table V the Biochemical Oxygen Demand of the efiluent from thepaper machine was determined and the control paper made without theprotein additive showed a considerably higher Biochemical Oxygen Demandin parts per million as compared with the paper made with the protein(Kasoy 200 D) additive. This reduction in Biochemical Oxygen Demandresulting from the manufacture of paper in accordance with the teachingsof the invention is of considerable importance in that stream pollutionlaws present severe restrictions on paper making activity where afurther increase in the Biochemical Oxygen Demand of the paper machineeffluent due to increased paper making capacity produces prohibitedstream pollution results. This, of course, means a severe and costlyrestriction to business expansion. With the novel method of theinvention, an increased retention of the finely divided pollutioncausing material in the pulp is obtained and the Biochemical 4 OxygenDemand of the paper machine effluent is sharply reduced as indicated inTable V.

While there has been described what at present is considered to bepreferred embodiment of the invention, it will be understood by thoseskilled in the art that various changes and modifications may be madetherein without departing from the invention and, therefore, it is theaim of the appended claims to cover all such changes and modificationsas fall Within the true spirit and scope of the invention.

Having thus described the invention, what is claimed 1. In a method oftreating cellulosic fibers comprising the steps of, preparing an anionicaqueous suspension of cellulosic fibers, colloidally dispersing anamphoteric protein in an acid solution to produce a cationic proteindispersion, mixing said cationic protein dispersion with said cellulosicfibers with the amount of said protein substantially less in proportionto the cellulosic fibers by weight the improvement of, adjusting the pHof the protein-fiber mixture to substantially the iso-electric point ofthe protein to complete the precipitation of the protein on the fibersof the paper pulp, and forming a paper web from the resulting paperstock.

2. In a method of treating cellulosic fibers comprising the steps of,preparing an anionic aqueous suspension of cellulosic fibers,colloidally dispersing an amphoteric protein in an acid solution toproduce a cationic protein dispersion, mixing said cationic proteindispersion with said cellulosic fibers, the improvement of limiting theamount of protein mixed in said mixing step to less than 10 of theweight of the cellulosic fibers in a bone dry state, adjusting the pH ofthe protein-fiber mixture to substantially the iso-electric point of theprotein to complete the precipitation of the protein on the fibers ofthe paper pulp and forming a paper web from the resulting paper stock.

3. In a method of treating cellulosic fibers comprising the steps 10f,preparing an anionic aqueous suspension of cellulosic fibers,colloidally dispersing an amphoteric protein in an acid solution toproduce a cationic protein dispersion, mixing said cationic proteindispersion with said cellulosic fibers, the improvement of limiting theamount of protein mixed in said mixing step to a range of between 0.1%to 5.0% of the weight of the cellulosic fibers in a bone dry state,adjusting the pH of the proteinfiber mixture to substantially thealso-electric point of the protein to complete the precipitation of theprotein on the fibers of the paper pulp and forming a paper web from theresulting paper stock.

4. In a method of treating cellulosic fibers comprising the steps of,preparing an anionic aqueous suspension of cellulosic fibers,colloidally dispersing an amphoteric protein in an acid solution in thepresence of heat at a pH within the range of 1.5 to 2.5 to produce acationic protein dispersion, mixing said cationic protein dispersionwith said cellulosic fibers with the amount of said proteinsubstantially less in proportion to the cellulosic fibers by weight theimprovement of, adjusting the pH of the protein-fibers mixture tosubstantially the isoelectric point of the protein to complete theprecipitation of the protein on the fibers of the paper pulp, andforming a paper Web from the resulting paper stock.

5. In a method of treating cellulosic fibers comprising the steps of,preparing an anionic aqueous suspension of cellulosic fibers,colloidally dispersing an amphoteric protein in an acid solution toproduce a cationic protein dispersion, mixing said cationic proteindispersion with said cellulosic fibers with the amount of said proteinsubstantially less in proportion to the cellulosic fibers by weight theimprovement of, adjusting the pH of the protein-fibers mixture with anacidifying composition to a pH within the range of 4.5 to 5.5 tocomplete the precipitation of the protein on the fibers of the paperpulp, and forming a paper web from the resulting paper stock.

6. In a method of treating cellulosic fibers comprising the steps of,preparing an anionic aqueous suspension of cellulosic fibers at a pHwithin the range of 6.5 to 7.5, colloidally dispersing an amphotericprotein in an aqueous acid solution in the presence of heat at a pHwithin the range of 1.5 to 2.5 to produce a cationic protein dispersion,mixing said cationic protein dispersion with said cellulosic fibers inan amount within the range of 0.5% to 1.5% of the weight of thecellulosic fibers in a bone dry state, the improvement of, addingpapermakers alum to the protein-fibers mixture to adjust the pH of themixture to a pH within the range of 4.5 to 5.0 to complete theprecipitation of the protein on the fibers of the paper pulp, andforming a paper web from the resulting paper stock.

7. In a method of treating cellulosic fibers comprising the steps of,preparing an anionic aqueous suspension of cellulosic fibers,colloidally dispersing a protein selected from the group consisting ofcasein, soybean protein and soybean meal in an acid solution to producea cationic protein dispersion, mixing said cationic protein dispersionwith said cellulosic fibers with the amount of said proteinsubstantially less in proportion to the cellulosic fibers by weight theimprovement of, adjusting the pH of the protein-fibers mixture tosubstantially the iso-electric point of the protein to complete theprecipitation of the protein on the cellulosic fibers, and forming apaper web from the resulting paper stock.

References Cited in the file of this patent UNITED STATES PATENTS1,622,496 Davidson et a1 Mar. 29, 1927 2,352,922 Thomas et al July 4,1944 2,559,848 Caldwell July 10, 1951 FOREIGN PATENTS 573,467 CanadaApr. 7, 1959

1. IN A METHOD OF TREATING CELLULOSIC FIBERS COMPRISING THE STEPS OF,PREPARING AN ANIONIC AQUEOUS SUSPENSION OF CELLULOSIC FIBERS,COLLOIDALLY DISPERSING AN AMPHOTERIC PROTEIN IN AN ACID SOLUTION TOPRODUCE A CATIONIC PROTEIN DISPERSION, MIXING SAID CATIONIC PROTEINDISPERSION WITH SAID CELLULOSIC FIBERS WITH THE AMOUNT OF SAID PROTEINSUBSTANTIALLY LESS IN PROPORTION TO THE CELLULOSIC FIBERS BY WEIGHT THEIMPROVEMENT OF, ADJUSTING THE PH OF THE PROTEIN-FIBER MIXTURE TOSUBSTANTIALLY THE ISO-ELECTRIC POINT OF THE PROTEIN TO COMPLETE THEPERCIPITATION OF THE PROTEIN